Figure 4

Predicted and measured concentrations of iron, hydrogen sulfide, hydrogen, and methane for diffuse fluids in the Tube Worm Pillar area. Hydrogen is strongly depleted over the entire period. Methane is enriched in the diffuse fluids, which may show methanogenesis in the subseafloor [13]. Until 1997, iron and H₂S concentrations are generally lower than predicted from conservative mixing. In November of 1997 predicted and measured concentration are similar to each other. In April of 2000 measured H₂S concentrations also correspond to the predictions from conservative mixing, but Fe-concentrations are higher than predicted in the diffuse fluid. Loss of Fe²⁺ and H₂S may be associated with precipitation of minerals. The surplus of measured Fe²⁺ in 2000 could indicate hydrogenotrophic iron reduction.